Process for the extraction of metal values and novel metal extractants

ABSTRACT

Metal values are extracted from aqueous solutions of metal salts containing halide or pseudo halide ions by pyrimidine, pyrazine or pyridazine derivatives bearing the substituent --(C═O.X) n  where X is the group --OR 1  or --NR 2  R 3  and n is 1, 2 or 3. R 1  is a hydrocarbyl group containing from 1 to 36 carbon atoms and R 2  and R 2  together contain from 1 to 36 carbon atoms. The molecule as a whole contains from 5 to 36 alkyl carbon atoms and may carry further optional substituents. The process is especially useful for the recovery of metals from leach solutions derived from sulphur-containing ores.

This invention relates to a process for the extraction of metal valuesfrom aqueous solutions of metal salts, and in particular to a processfor the extraction of metal values from aqueous solutions in thepresence of halide anions.

The use of solvent extraction techniques for the hydrometallurgicalrecovery of metal values from metal ores has been practised commerciallyfor a number of years. For example copper may be recovered from oxideores or from ore tailings by treating the crushed ore with sulphuricacid to give an aqueous solution of copper sulphate which issubsequently contacted with a solution in a water-immiscible organicsolvent of a metal extractant whereby the copper values are selectivelyextracted into the organic phase.

The application of solvent extraction techniques to aqueous solutionscontaining halide anions however has presented numerous technicalproblems. For example copper bearing sulphur-containing ores such aschalcopyrite may be leached using ferric chloride or cupric chloridesolutions, but the solvent extraction of the resultant leach solutionspresents formidable difficulties.

The present invention provides a process for the extraction of metalvalues from aqueous solutions containing halide ions by the use of metalextractants whose several properties meet the stringent requirementsimposed on the extractant by the system.

According to the present invention there is provided a process forextracting metal values from aqueous solutions of metal salts containinghalide or pseudo halide anions which comprises contacting the aqueoussolution with a solution in a water-immiscible organic solvent of asubstituted pyrimidine pyrazine or pyridazine of formula: ##STR1##wherein

X is the group --OR₁ or --NR₂ R₃, R₁ being a hydrocarbyl groupcontaining from 1 to 36 carbon atoms and R₂ and R₃ separately beinghydrogen or a hydrocarbyl group, and R₂ and R₃ together containing from1 to 36 carbon atoms;

n is 1, 2 or 3; and

Y represents one or more groups which may separately be hydrogen,halogen, optionally substituted alkyl, optionally substituted aryl,alkoxy, aryloxy, aralkyl, carboxylic acid, cyano, and nitro;

provided that there is present in the molecule a total number of from 5to 36 alkyl carbon atoms,

The 5 to 36 alkyl carbon atoms which must be present in the molecule maybe distributed between the groups R₁ and Y and the groups R₂, R₃ and Yrespectively. Thus if Y is hydrogen or is a substituent containing noalkyl carbon atoms, then R₁ must contain from 5 to 36 alkyl carbon atomsor R₂ and R₃ together must contain from 5 to 36 carbon atomsrespectively. However, if Y is a substituent containing one or morealkyl carbon atoms, the number of alkyl carbon atoms present in R₁ andin R₂ and R₃ respectively may be reduced accordingly.

Preferably at least one position ortho to one of the two nitrogen atomsin the pyrimidine, pyrazine or pyridazine ring is free from bulkysubstituents and preferably is free from any substituent. It isespecially preferred that both positions ortho to at least one of thenitrogen atoms are free from bulky substituents, and preferably are freefrom any substituent. There is thus a general preference that one of thetwo nitrogen atoms in the pyrimidine, pyrazine or pyridazine ring issterically unhindered, whilst the other nitrogen atom is stericallyhindered by one or more adjacent substituents.

When n is 2 or 3, the substituent --X is the respective groups --COX maybe the same or different. For example when n is 2, the two groups --COXmay be --COR₁ and COR₁ ' respectively where R₁ and R₁ ' are bothhydrocarbyl groups each containing from 1 to 36 carbon atoms, providedthat the total number of alkyl carbon atoms in the molecule as a wholeis from 5 to 36. As examples of suitable pyrazines wherein n is 2, theremay be mentioned alkyl esters of 2,6-dicarboxypyrazine. As examples ofsuitable pyrimidines wherein n is 2, there may be mentioned alkyl estersof 4,5-dicarboxypyrimidine. As examples of suitable pyridazines whereinn is 2 there may be mentioned alkyl esters of 4,5-dicarboxypyridazine.

When n is 1, the group --COX is preferably located in the -5 position inthe pyrimidine ring, since we have found that such compounds generallyhave superior hydrolytic stability. In the pyrazine ring the substituent--COX is of necessity in the -2 position.

Preferably the group(s) --Y are hydrogen or, more preferably, one ormore alkyl groups, for example one or more lower alkyl groups or are oneor more optionally substituted aryl groups. As optionally substitutedaryl groups there may be mentioned the phenyl group and the phenyl groupcarrying as optional substituent one or more lower alkyl groups or loweralkoxy groups or one or more halogen atoms or one or more carboxylicacid or carboxylic acid ester groups. The presence of, for example analkyl substituent, on the aryl group may provide enhanced solubility ofthe reagent in the water-immiscible organic solvent or may permit theuse of a relatively shorter alkyl chain in the group --OR₁.

Pyrimidine compounds of the present invention having the group --COX inthe preferred -5 position preferably have a substituent --Y in the -4(or the equivalent -6) position, thereby increasing the steric hindranceof the nitrogen in the -3 (or the equivalent -1) position.

Similarly, pyrazine compounds of the present invention may have asubstituent --Y in the -6 position to hinder the reactivity of thenitrogen in the -1 position, thereby favouring the formation of a metalcomplex through the nitrogen in the -4 position.

The substituted pyrimidine pyrazine and pyridazine compounds of thepresent invention may be prepared by conventional means. For examplewhen X is the group --OR₁, they may be prepared by the reaction of theappropriate pyrimidine pyrazine or pyridazine carboxylic acid with theappropriate alcohol to form the desired ester. Alternatively, the loweresters, for example methyl or ethyl esters may be subjected to esterexchange reactions with higher alcohols, or the acid chlorides may bereacted with the appropriate alcohol or phenol.

When the group X is --OR₁, R₁ may for example be an alkyl group, forexample an octyl, nonyl, decyl, dodecyl, tridecyl, pentadecyl, hexadecylor octadecyl group or a higher alkyl group. R₁ may for example be acyclo alkyl group such as cyclohexyl. R₁ may for example be an aryl,alkyaryl or alkoxyaryl group for example p-nonylphenyl orp-dodecylphenyl.

To achieve good solubility of the compound in preferred organicsolvents, the alkyl solubilising group(s) (for example R₁) arepreferably branched alkyl group(s) or a mixture (including an isomericmixture) of branched alkyl groups. It is especially preferred that themolecule contains a total of from 9 to 24 alkyl carbon atoms.

Highly branched alkyl groups may be usefully derived from branchedalcohols prepared by the Guerbet and Aldol condensations. Such alcoholsare characterised by branching at the position beta to the hydroxylgroup and have the general formula: ##STR2## wherein R₄ and R₅ are bothalkyl groups and R₄ contains two fewer carbon atoms than R₅. R₄ and R₅may be straight chain or branched chain alkyl groups and may be isomericmixtures of alkyl groups. A mixture of highly branched alcohols may beobtained by Guerbrt or Aldol condensations of mixtures of alcohols andaldehydes respectively. By way of example, good solubility in preferredorganic solvents is conferred on the pyrimidine pyrazine or pyridazinecompounds wherein R₁ is derived from 2-hexyldecanol, 2-octyldodecanoland most especially commercial isooctadecanol prepared by thedimerisation of commercial nonanol or commercial nonaldehyde andbelieved to consist essentially of a mixture of geometrical isomers ofthe compound: ##STR3##

Alcohols of formula (iv) above, although branched, are all primaryalcohols. For pyrazine compounds especially, there may be advantages inemploying a group --R₁ derived from a branched secondary or tertiaryalcohol, for example 3,9-diethyl-tridecan-6-ol.

The amide group --NR₂ R₃ may be secondary (R₃ is hydrogen) or, morepreferably, tertiary. R₂ and R₃, which may be the same or different, maybe groups of the type indicated above for R₁. R₂ and R₃ taken togetherpreferably contain from 15 to 36 carbon atoms. Thus R₃ may be forexample a lower alkyl group, for example a methyl group, provided R₂ iscorrespondingly larger. R₂ and R₃ taken together are preferably alkylgroups containing a total of from 15 to 36 carbon atoms. For tertiaryamines, sufficient solubility in preferred organic solvents maygenerally be achieved if R₂ and R₃ are straight chain or branched chainalkyl groups. However for secondary amides (R₂ is hydrogen), R₃ ispreferably a branched chain alkyl group. The total number of alkylcarbon atoms in the molecule is from 5 to 36, and in consequence ifalkyl carbon atoms are present in the substituent Y, the number of alkylcarbon atoms in R₂ and R₃ may be correspondingly reduced without loss ofsolubility.

The process of the present invention may be applied to the extractionfrom aqueous solutions containing halide or pseudohalide ion of anymetal capable of forming a stable halide or pseudohalide containingcomplex with the pyrimidine pyrazine or pyridazine compound in thewater-immiscible organic solvent. Examples of such metals includecopper, cobalt, cadmium and zinc. The process of the present inventionis especially suitable for the solvent extraction of copper from aqueoussolution obtained by the halide or psuedohalide leaching of sulphurcontaining ores, for example from solutions obtained by the leaching ofores such as chalcopyrite with aqueous ferric chloride or cupricchloride solutions.

It will be appreciated that the process of the present invention may beincorporated into a wide variety of different methods for the overallrecovery of metals from their ores or from other metal-bearing sources.Details of these methods will vary depending on the metal concerned andthe nature and composition of the leach solution. By way of example, anintegrated process which is especially suitable for leach solutionscontaining high levels of cupric ion is described in European PatentApplication No. 0 057 797.

The extraction process of the present invention may be represented by anequation such as the following:

    2L.sub.org +M.sup.++.sub.aq +2Cl.sup.-.sub.aq ⃡(L.sub.2 MCl.sub.2).sub.org

where M is a divalent metal ion such as copper or zinc.

This equation is a grossly oversimplified representation of a verycomplex process and is not to be taken as in any way limiting the scopeof the present invention, but it serves to illustrate the formation of aneutral organic phase complex of the divalent metal and the extractant(L) which is believed to predominate in the process of the presentinvention. The equation illustrates the reversible nature of theextraction, whereby the complex of the metal and the extractant in theorganic phase can be stripped to return the purified and concentratedmetal ion into an aqueous phase. Stripping may take place for example oncontact of the organic phase containing the metal/extractant complexwith water or with the aqueous solution from the metal recovery (forexample electrowinning) stage which is depleted in the metal and in thehalide ion.

A further property which is of importance for an extractant in theprocess of the present invention is the absence of significantprotonation by the acidic leach liquor. Such protonation may berepresented by an equation such as:

    L.sub.org +H.sup.+.sub.aq +Cl.sup.- aq⃡(LH.sup.+ Cl.sup.-).sub.org

where L is the extractant. Such protonation of the ligand carrieshydrochloric acid into the organic phase and builds up an excessivechloride ion concentration on the strip side. Preferred reagents of thepresent invention combine a high affinity for copper with an especiallylow acid transfer into the organic phase. Such reagents are especiallyuseful for the treatment of metal solutions having high concentrationsof acid/halide ion.

Examples of suitable water-immiscible organic solvents are aliphatic,aromatic and alicyclic hydrocarbons, chlorinated hydrocarbons such asperchloroethylene, trichloroethane and trichloroethylene. Mixtures ofsolvents may be used. Especially preferred in conventionalhydrometallurgical practice are mixed hydrocarbon solvents such as highboiling, high flash point petroleum fractions (for example kerosene)with varying aromatic content. In general, hydrocarbon solvents having ahigh aromatic content, for example AROMASOL H which consists essentiallyof a mixture of trimethylbenzenes and is commercially available fromImperial Chemical Industries PLC (AROMASOL is a trade mark) or SOLVESSO150 commercially available from Esso (SOLVESSO is a trade mark), providea higher solubility for the extractant and its metal complex, whilstkerosene having a relatively low aromatic content, for example ESCAID100 which is a petroleum distillate comprising 20% aromatics, 56.6%paraffins and 23.4% napthenes commercially available from ESSO (ESCAIDis a trade mark) may in certain cases improve the hydrometallurgicalperformance of the extractant. Factors influencing the solubility of theextractant and its metal complex are complicated, but in generalextractants having highly branched substituents and/or an isomericmixture of substituents have comparatively high solubility. Theconcentration of the extractant in the water-immiscible organic solventmay be chosen to suit the particular leach solution to be treated.Typical values of extractant concentration in the organic phase arebetween about 0.1 to 2 Molar, and an especially convenient range is from0.2 to 1.0 Molar in the organic solvent.

As illustrated by the examples, the extractants of the present inventionprovide a range of properties so that the optimum extractant may beselected for a given leach solution and extraction conditions.

In general we have found that pyrazines, and in particular thosesubstituted pyrazines shown in the examples, have excellent propertiesin terms of a relatively high "strength" (ability to extract relativelyhigh levels of copper from the leach solution) which is combined with anexcellent resistance to proton transfer, even in more acidic leachsolutions. In general, however, the substituted pyrazines of theinvention and their metal complexes have insufficient solubility inpreferred kerosene solvents having a relatively low aromatic content tooperate at the higher end of the preferred range of extractantconcentration. They are therefore most suitable for use at lowerconcentration, for example at concentrations below 0.5M, and in solventshaving a higher aromatic content.

In general we have found that pyrimidines have good solubility inpreferred solvents, and a good resistance to long-term hydrolysis underthe stringent conditions of the solvent extraction process. Theproperties of individual pyrimidines may vary. Thus esters of4-methylpyrimidine-5-carboxylic acid, for example the esters of Example1 and 3, are excellent for use with leach solutions in the middle of therange of chloride ion concentration (for example about 4 to 7 Molar inchloride ion). Esters of 4-phenylpyrimidine-5-carboxylic acid, forexample those of Example 6, are weak ligands which are especially usefulfor leach solutions having a high chloride ion concentration (above 7Molar in chloride ion), particularly when the acidity is also high (0.5Mand higher in HCl). Under these conditions, the ester of4-phenylpyrimidine-5-carboxylic acid shows good copper extraction withrelatively low acid transfer. The loaded extractant is readily strippedto recovery the copper.

Certain pyrimidines pyrazines and pyridazines for use in the presentinvention are novel compounds and the present invention includes suchnovel compounds.

The invention is illustrated by the following examples in which allparts and percentages are by weight unless otherwise stated.

EXAMPLE 1

The 2-hexyldecyl ester of 4-methylpyrimidine-5-carboxylic acid wasprepared as follows:

The ethyl ester of 4-methylpyrimidine-5-carboxylic acid was preparedusing the method described in Helv. Chim. Acta 41 1806 (1958). Thisproduct (27 g) was heated with 2-hexyldecanol (34.5 g) at 160° C. in thepresence of tetrabutyl titanate (3 drops). Over the next 48 hours afurther 9 drops of tetrabutyl titanate was added, and the temperaturewas then raised to 190° C. Heating continued for a further 23 hours.Distillation of the product gave an oil having a boiling point of 180°C. at 0.05 mm of mercury. The structure of the product was confirmed byinfrared and n.m.r. analysis.

The ability of the 2-hexyldecyl ester of 4-methylpyrimidine-5-carboxylicacid to extract copper from aqueous solution containing chloride ion wasinvestigated by the following general method:

An aqueous solution was prepared which was 0.1M in cupric chloride (6.35gpl copper), and 0.1M in hydrochloric acid and which contained 250 gplof calcium chloride dihydrate. This solution was then agitated for 1minute with an equal volume of a solution which was a 0.2M solution ofthe extractant in SOLVESSO 150. The layers were allowed to separate andsettle, and were separately analysed for copper content. The transfer ofcopper from the aqueous to the organic phase was calculated as thepercentage of the ligand taken up as the copper complex (assuming thecomplex L₂ CuCl₂). The transfer of hydrochloric acid from the aqueoussolution into the organic solution was calculated as the percentage ofligand that was protonated. The test was repeated using differentmolarities of hydrochloric acid and different concentrations of calciumchloride. The test was then repeated using ESCAID 100 as solvent inplace of SOLVESSO 15. The results are presented in Table 1. The resultsshow that the ligand has an excellent affinity for copper combined witha low transfer of acid even at high chloride ion/acid concentrations.The ligand shows excellent copper transfer when ESCAID 100 is used assolvent.

EXAMPLE 2

The 2-hexyldecyl ester of 2,4-dimethylpyrimidine-5-carboxylic acid wasprepared from the corresponding ethyl ester and 2-hexyldecanol using themethod of Example 1. The compound was evaluated as an extractant forcopper using the procedure of Example 1, and the results are presentedin Table 1. The results show that the ligand has substantial affinityfor copper.

EXAMPLE 3

The isooctadecyl ester of 4-methylpyrimidine-5-carboxylic acid wasprepared from the corresponding ethyl ester and commercialisooctadecanol using the method of Example 1. The compound was evaluatedas an extractant for copper using the procedure of Example 1, and theresults are presented in Table 1. The results show that the ligand hasgood affinity for copper combined with a relatively low acid transfereven at high chloride ion/acid concentrations.

EXAMPLE 4

The good solubility and stripping properties of the product of Example 3were demonstrated as follows:

A solution of the ligand which was 0.48 molar in ESCAID 100 was loadeduntil the copper concentration in the organic phase reached 13.7 gpl(90% of the theoretical maximum) by shaking with fresh portions of anaqueous solution which was 0.1 molar in CuCl₂ and 0.1 molar inhydrochloric acid and which contained 700 gpl CaCl₂.2H₂ O.

The organic phase was separated from the aqueous phase and allowed tostand for 10 months at ambient temperature. No precipitation or phaseseparation was observed during this period. The organic phase solutionwas then stripped by shaking with an equal volume of water. The aqueoussolution was analysed by titration, and it was found that more than 95%of the copper initially present in the loaded organic solution hadtransferred to the aqueous phase.

EXAMPLE 5

The 2-hexyldecyl ester of pyrazine-2-carboxylic acid was prepared asfollows:

Pyrazine-2-carboxylic acid (12.4 g), thionyl chloride (17.85 g) toluene(100 ml) and dimethyl formamide (3 drops) were refluxed together for oneand a half hours during which time a clear red solution formed. Thesolvent and excess thionyl chloride were removed under vacuum, and2-hexyldecanol (21.8 g) was added, with the evolution of heat. Theproduct was taken up in dichloromethane (200 ml) and the solution washedsuccessively with water, sodium carbonate, dilute hydrochloric acid andwater once more. The solution was dried over magnesium sulphate andcarbon screened. On removal of the solvent the product was distilled togive 22.33 g of an oil having a boiling point of 190° C. at 0.4 mm ofmercury pressure. The structure was confirmed by infrared and n.m.r.analysis.

The compound was evaluated as an extractant for copper using theprocedure of Example 1, and the results are presented in Table 1. Theresults show that the ligand has a very good affinity for coppercombined with an exceptionally low acid transfer even at high chlorideion/acid concentrations.

EXAMPLE 6

The isooctadecyl ester of pyrazine-2-carboxylic acid was prepared frompyrazine-2-carboxylic acid and isooctadecanol using the method ofExample 5.

The compound was evaluated as an extractant for copper using theprocedure of Example 1, and the results are presented in Table 1. Theresults show that the ligand has a very good affinity for coppercombined with an exceptionally low acid transfer even at high chlorideion/acid concentrations.

EXAMPLE 7 (1) Preparation of Ethoxy methylene ethyl benzoylacetotate

A mixture of triethyl orthoformate (177.6 parts ), ethyl benzoylacetate(192 parts) and glacial acetic acid (6 parts) was stirred and heated at140° to 150° C. for about 41/2 hours whilst the ethanol generateddistilled off into a receiver. The residue was distilled and thefraction distilling at 164°-170° C. at 0.2 mm of mercury pressure,ethoxy methylene ethyl benzoylacetate (137.3 parts), was collected.

(2) Preparation of 4-phenyl-5-ethoxycarbonylpyrimidine

Formamidine acetate (57.2 parts) was added to a stirred solution ofsodium (12.65 parts) in methylated spirits (234 parts) and the stirringwas continued for half an hour. Ethoxy methylene ethyl benzoylacetate(124 parts) was added and the temperature was allowed to rise to 40° to50° C. The mixture was heated under reflux for 2 hours and the solventwas then distilled off. The residue was distilled and the fractionboiling at 122° to 132° C. under 0.2 mm of mercury pressure,4-phenyl-5-ethoxycarbonylpyrimidine (77.8 parts), was collected.

(3) Preparation of the isooctadecyl ester of4-phenylpyrimidine-5-carboxylic acid

A mixture of 4-phenyl-5-ethoxycarbonylpyrimidine (68.4 parts),isooctadecanol (85.05 parts) and tetrabutyltitanate (0.85 parts) wasstirred and heated at 160° C. to 170° C. for 48 hours, allowing theethanol produced to distil off. Excess alcohol was removed and theproduct (120 parts) was the isodecyl ester of4-phenylpyrimidine-5-carboxylic acid.

The product was evaluated as an extractant for copper using theprocedure of Example 1, and the results are presented in Table 1. Theresults show that this compound is a "weak" ligand which has goodresistance to acid transfer, and is especially suitable for use withfeed solutions of high chloride ion concentration.

In a further test to evaluate the use of the ligand in more concentratedsolution in the water-immiscible solvent, a 0.5 Molar solution of theproduct in ESCAID 100 was twice contacted with portions of an aqueousfeed at an organic:aqueous ratio of 1:2. The aqueous feed solution hadhigh acidity and high chloride ion concentration, and was prepared bydissolving cupric chloride dihydrate (13.4 g), calcium chloridedihydrate (57.7 g) and 10M hydrochloric acid (b 5.0 cm³) in water andadjusting the volume to 100 cm³. The organic solution was analysed afterthe extraction and was found to contain 12.9 gpl of copper (81% of thetheoretical maximum uptake). The clear greenish blue loaded organicsolution showed no precipitation of insoluble matter on standing for aperiod of 5 months.

EXAMPLE 8

A 0.5 molar solution in ESCAID 100 of 4-phenylpyrimidine-5-carboxylicacid (prepared as in Example 7) was used to extract copper to a loadingof 12.57 gpl (as CuCl₂). The loaded extractant solution was stripped byequilibration with an aqueous solution containing 27.26 gpl copper (asCuCl₂) and 5 gpl hydrochloric acid. At a ratio of organic phase toaqueous phase of 1:1 by volume, the equilibrium copper concentrationswere: 0.57 gpl of copper in the organic phase and 39.39 gpl copper inthe aqueous phase. At a ratio of organic phase to aqueous phase of 2:1by volume, the equilibrium copper concentrations were: 0.89 gpl ofcopper in the organic phase and 50.45 gpl copper in the aqueous phase.

EXAMPLE 9

A 0.5 molar solution in ESCAID 100 of 4-phenylpyrimidine-5-carboxylicacid (prepared as in Example 7) was used to extract copper to a loadingof 11.50 gpl (as CuCl₂). The loaded extractant solution was stripped byequilibration with an aqueous soluton containing 1.0 gpl copper (asCuCl₂) 58.5 gpl sodium chloride and 1 gpl hydrochloric acid. At a ratioof organic phase to aqueous phase of 1:1 by volume, the equilibriumcopper concentrations were: 0.25 gpl of copper in the organic phase and12.26 gpl copper in the aqueous phase. At a ratio of organic phase toaqueous phase of 2:1 by volume, the equilibrium copper concentrationswere: 0.64 gpl of copper in the organic phase and 22.68 gpl copper inthe aqueous phase.

EXAMPLE 10

The 3,9-diethyl-6-tridecyl ester of pyrazine-2-carboxylic acid wasprepared from pyrazine-2-carboxylic acid and 3,9-diethyl-tridecan-6-ol(a secondary alcohol) using the general method of Example 5. The producthad a boiling range of 165° to 170° C. at 0.2 mm of mercury pressure.

The product was evaluated as an extractant for copper using theprocedure of Example 1, and the results are presented in Table 1.

EXAMPLE 11

N,N-bis(2'-ethylhexyl)pyrazine-2-carboxamide was prepared frompyrazine-2-carboxylic acid and bis(2-ethylhexyl)amine by the generalmethod of Example 5, the amine being used in place of the alcohol. Thecompound had a boiling range of 155° to 160° C. at 0.2 mm pressure ofmercury.

The product was evaluated as an extractant for copper using theprocedure of Example 1, and the results are presented in Table 1.

EXAMPLE 12

N,N-diisononylpyrazine-2-carboxamide was prepared frompyrazine-2-carboxylic acid and commercial di-isononylamine using thegeneral method of Example 11. The product had a boiling range of163°-165°° C. at 0.15 mm of mercury pressure.

The product was evaluated as an extractant for copper using theprecedure of Example 1, and the results are presented in Table 1.

EXAMPLE 13

The tridecyl ester of 4-phenylpyrimidine-5-carboxylic acid was preparedfrom 4-phenyl-5-ethoxycarbonylpyrazine and commercial tridecanol usingthe general procedure of Example 7. The product had a boiling range of160°-170° C. at 0.2 mm pressure of mercury.

The product was evaluated as an extractant for copper using theprocedure of Example 1, and the results are presented in Table 1.

EXAMPLE 14

The 2-hexyldecyl ester of 4-phenylpyrimidine-5-carboxylic acid wasprepared from 2-hexyldecanol and 4-phenyl-5-ethoxycarbonylpyrimidineusing the general procedure of Example 7. The product had a boilingrange of 206°-208° C. at 0.2 mm pressure of mercury.

The product was evaluated as an extractant for copper using theprocedure of Example 1, and the results are presented in Table 1.

EXAMPLE 15

The isooctadecyl ester of 4-(4'-methoxyphenyl)pyrimidine-5-carboxylicacid was prepared using the general method of Example 7 from4-methoxybenzoyl chloride, ethyl acetoacetate and sodium hydroxide viathe intermediates ethyl (4-methoxybenzyl)acetate and the ethyl ester of4-(4'-methoxyphenyl)pyrimidine-5-carboxylic acid. The product had aboiling point of 200° to 205° C. at 0.1 mm of mercury pressure. Theproduct was evaluated as an extractant for copper using the procedure ofExample 1 and the results are presented in Table 1.

EXAMPLE 16

The isooctadecyl ester of 4-(2'-chlorophenyl)pyrimidine-5-carboxylicacid was prepared using the general method of Example 7 from2-chlorobenzoyl chloride, ethyl acetoacetate and sodium hydroxide viathe intermediates ethyl (2-chlorobenzoyl)acetate and the ethyl ester of4-(2'-chlorophenyl)pyrimidine-5-carboxylic acid. The product had aboiling point of 192° C. at 0.1 mm of mercury pressure. The product wasevaluated as an extractant for copper using the procedure of Example 1and the results are presented in Table 1.

EXAMPLE 17

The isooctadecyl ester of 4-carboxypyridazine was prepared as follows:

4,5-Dicarboxypyridazine (12 parts), isooctadecanol (50 parts), toluene(20 parts) and 4-methylbenzene sulphonic acid (2 parts) were stirred andboiled under reflux below a Dean-Stark trap initially filled withtoluene. With these proportions of reactants, the temperature of thereaction mixture was 148° C. and partial decarboxylation as well asesterification of the acid took place. After 1.5 hours, when 0.75 ml ofwater had collected in the trap, the reaction mixture was cooled,diluted with petroleum ether (b.p. 60°-80° C., 50 parts) and washed withwater. The product was distilled under reduced pressure and the fractiondistilling at 180°-190° C. at 0.4 mercury pressure was collected. 3.6parts of product were obtained having a purity of 84% as measured bypotentiometric titration with perchloric acid in acetic acid/aceticanhydride medium. The product was evaluated as an extract and using themethod of Example 1, and the results are listed in Table 1.

EXAMPLE 18

The isodecyl ester of 4-carboxypyridazine was prepared using the generalmethod of Example 17 from isodecanol and 4,5-dicarboxypyridazine. Theproduct has a boiling range of 150°-160° C. at 0.4 mm of mercurypressure. The product was evaluated as an extractant for copper by theprocedure of Example 1, and the results are listed in Table 1. Theresults show that this compound has inferior solubility to thecorresponding isooctadecyl ester of Example 17.

EXAMPLE 19

The bis(isodecyl)ester of 4,5-dicarboxypyridazine was prepared asfollows:

4,5-dicarboxypyridazine (16 parts), isodecanol (70 Parts), toluene (50parts) and 4-methylbenzene sulphonic acid (2.5 parts) were stirred andheated for 5 hours under reflux below a Dean-Stark trap initially filledwith toluene. With these proportions the reaction temperature was 128°C., and 1.6 parts of water collected in the trap. The mixture wascooled, diluted with petroleum spirit (70 parts b.p. 60°-80° C.), washedwith water and distilled under reduced pressure. A small quantity of theisodecyl ester of 4-carboxypyridazine boiling at 155° C. at 0.4 mm ofmercury pressure was collected and this was followed by thebis(isodecyl)ester of 4,5-dicarboxypridazine boiling at 235°-240° C. ata pressure of 0.4 mm of mercury. The product (5.6 parts) had a purity of98% as estimated by titration with perchloric acid and was evaluated asan extractant for copper using the procedure of Example 1. The resultsare listed in Table 1.

EXAMPLE 20

The ease with which the compounds of the invention may in general bestripped of copper was demonstrated as follows:

A 0.2 molar solution in SOLVESSO 150 of the respective ligands ofExamples 7, 10, 11, 14, 16 and 17 was loaded by contacting with an equalvolume of 0.1 molar aqueous CuCl₂ which was 0.1 molar in hydrochloricacid and contained 700 gpl CaCl₂.2H₂ O. The resultant loading were asrecorded in the appropriate column of Table 1. The loaded organic phasewas separated and shaken with an equal volume of water, and the waterlayer was analysed for copper. In every case, more than 97% of thecopper originally present in the loaded organic phase was found to havetransferred into the aqueous phase.

                  TABLE 1                                                         ______________________________________                                                                 % Uptake from                                               HCl    CaCl.sub.2.2H.sub.2 O                                                                    0.1M CuCl.sub.2                                      Example  Molarity (g/l)      Copper protonation                               ______________________________________                                        1.       0.1      250        18     0                                         (Solvent:                                                                              0.1      500        42     0                                         SOLVESSO 0.1      700        63.5   0.5                                       150)     1.0      250        32     0.5                                                1.0      500        53     2                                                  1.0      700        61     27                                        1.       0.1      250        24     0                                         (Solvent:                                                                              0.1      700        70     0                                         ESCAID   1.0      250        39     0                                         100)     1.0      700        65     31                                        2.       0.1      700        22     13                                        (Solvent:                                                                              1.0      700        53     82                                        SOLVESSO                                                                      150)                                                                          3.       0.1      700        55     2                                         (Solvent:                                                                              1.0      350        21     1                                         SOLVESSO 1.0      700        55     21                                        150)                                                                          5.       0.1      700        43     0                                         (Solvent:                                                                              1.0      250        14     0                                         SOLVESSO 1.0      700        47     0.5                                       150)                                                                          6.       0.1      700        39     0                                         (Solvent:                                                                              1.0      250        10     0                                         SOLVESSO 1.0      700        43     1                                         150)                                                                          7.       0.1      250        4      0                                         (Solvent:                                                                              0.1      700        37     1.5                                       SOLVESSO 1.0      250        6      0                                         150)     1.0      700        41     9                                         7.       0.1      250        2      0.5                                       (Solvent:                                                                              0.1      700        51     1                                         ESCAID   1.0      250        6      0.5                                       100)     1.0      700        55     7.5                                       10.      0.1      250        6      0                                         (Solvent:                                                                              0.1      700        46     0                                         SOLVESSO 1.0      250        12     0                                         150)     1.0      700        49     1.5                                       11.      0.1      250        0      0.25                                      (Solvent:                                                                              0.1      700        41     0.25                                      SOLVESSO 1.0      250        4      0.25                                      150)     1.0      700        47     5.5                                       12.      0.1      250        10     0.25                                      (Solvent:                                                                              1.0      700        85     11                                        SOLVESSO                                                                      150)                                                                          13.      0.1      250        2      0                                         Solvent: 1.0      700        47     12                                        SOLVESSO                                                                      150)                                                                          14.      0.1      250        3      0                                         (Solvent:                                                                              1.0      700        47     9                                         SOLVESSO                                                                      150)                                                                          15.      0.1      250        3      0                                         (Solvent:                                                                              1.0      700        58     8                                         SOLVESSO                                                                      150)                                                                          16.      0.1      250        0      0                                         (Solvent:                                                                              0.1      700        16     0.5                                       SOLVESSO 1.0      250        2      0                                         150)     1.0      700        20     2.5                                       17.      0.1      250        11     0                                         (Solvent:                                                                              0.1      700        86     1                                         SOLVESSO 1.0      700        80     41                                        150)                                                                          18.      0.1      250        16     0                                         (Solvent:                                                                              0.1      700        third liquid phase formed                        SOLVESSO                                                                      150)                                                                          19.      0.1      250        7      0                                         (Solvent:                                                                              0.1      700        67     2                                         SOLVESSO 1.0      700        57     15                                        150)                                                                          ______________________________________                                    

I claim:
 1. A process for extracting metal values from aqueous solutions of metal salts containing halides or pseudo halide anions which comprises contacting the aqueous solution with a solution in a water-immiscible organic solvent of a substituted pyrimidine, pyrazine or pyridazine of formula: ##STR4## wherein X is the group --OR₁ or --NR₂ R₃, R₁ being a hydrocarbyl group containing from 1 to 36 carbon atoms and R₂ and R₃ separately being hydrogen or a hydrocarbyl group, and R₂ and R₃ together containing from 1 to 36 carbon atoms;n is 1, 2 or 3; and Y represents one or more optionally substituted phenyl groups,provided that there is present in the molecule a total number of from 5 to 36 alkyl carbon atoms.
 2. A process according to claim 1 wherein Y represents a phenyl group having one or more substituents selected from the group consiting of a lower alkyl group, a lower alkoxy group, a carboxylic acid group, a carboxylic acid ester group and a halogen atom.
 3. A process according to claim 1 or claim 2 wherein there is present in the molecule a total number of from 9 to 24 alkyl carbon atoms.
 4. A process according to claim 1 or claim 2 wherein n is 1, X is the group --OR₁ and R₁ is a branched chain alkyl group containing from 9 to 24 carbon atoms.
 5. A process according to claim 1 or 2 wherein n is 1 or 2, X is the group --OR₁ and R₁ is the group ##STR5## wherein R₄ and R₅ are alkyl groups and R₄ contains two fewer carbon atoms than R₅.
 6. A process according to claim 1 or claim 2 wherein n is 1, X is the group --OR₁, and R₁ is isodecyl, tridecyl, 2-hexyldecyl, isooctadecyl or 3,9-diethyl-6-tridecyl.
 7. A process according to claim 1 or claim 2 wherein there is employed a substituted pyrimidine; n is 1; the group --COX is located in the -5 position on the pyrimidine ring; and the group --Y is located in the -4position.
 8. A process according to claim 1 wherein n is 1, X is the group --NR₂ R₃, and R₂ and R₃ are alkyl groups which taken together contain a total of from 15 to 36 carbon atoms. 